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Gypsy moth traps dot area as state hunts for insect invaders

August 30, 2011

By Tom Corrigan

Hung from the trunk of at least one tree on Issaquah’s Front Street South near Our Savior Lutheran Church, the bright green traps definitely can grab your attention.

State workers placed the traps, which look somewhat like triangular-shaped boxes, sometime in late July. And the traps are only harmful if you happen to be a gypsy moth, said Mike Louisell, a public information officer with the state Department of Agriculture.

All in all, according to the state, some 20,000 gypsy moth traps went up around Washington in the last month or so. They are a key part of an annual effort to prevent gypsy moths from establishing themselves in Washington. The traps are hung annually in residential areas, as well as business districts and rural stretches.

Louisell said the traps are put up somewhat randomly, that the presence of the traps doesn’t necessarily mean the presence of gypsy moths. Because of its size and some risk factors, King County gets a large number of the traps. Those risk factors include the Port of Seattle, Louisell said. The unwanted moths easily can end up as stowaways aboard incoming ships.

The state is very serious about keeping the moths out of Washington, Louisell added. State information argues the moths are among the most dangerous of potential insect invaders because they are among the most voracious. They feed on the foliage of 500 different species of trees and shrubs. Nationwide, economic losses caused by the gypsy moth have averaged $30 million a year for the past 20 years, according to the U.S. Department of Agriculture. In a five-year period, the number of defoliated acres increased from 251,000 to 1.6 million where the moths struck.

What to know

Still, to put things in perspective, Louisell said the numbers of moths found in Washington, and specifically in King County, have remained small.

In 2009, the state found only two moths in all of King County. Last year, officials found seven, but Louisell said they also found a gypsy moth egg mass in Puyallup near the South Hill Mall.

When it comes to gypsy moths, a breeding population is what the state fears most. The Puyallup find prompted the first use of gypsy moth insecticides in the state since 2007. Working at night, workers sprayed insecticide in a corner of South Hill’s parking lot. The treatments were conducted over a period of several weeks. The spraying was timed to coincide with the development of gypsy moth caterpillars into actual moths.

According to information released by the state, South Hill will receive extra traps this summer to determine whether the spraying worked as planned. Louisell said the state only declares a spray treatment successful if no moths appear in the targeted area for two years in a row.

The green traps set up in Issaquah and elsewhere contain a sex pheromone that attracts male moths. Inside the traps is a sticky surface similar to flypaper. Louisell said the traps are checked every few weeks before being taken down permanently in September.

“They are very common,” he said, adding his department routinely handles calls and questions about the traps.